The overall objective of the project is to contribute to knowledge about the regulation of calcium metabolism by clarifying the role of various hormones, known and as yet unrecognized, thereby improving measures for the prevention, diagnosis and treatment of calcium-related diseases. Specific objectives: 1. Search for an adrenal factor to explain the effect of prior adrenalectomy to reduce the fall in serum Ca after parathyroidectomy in rats. Experiments will discriminate between the adrenal cortex, adrenal medulla, and surgical trauma as an explanation of the effect. 2. Clarify the physiological function of calcitonin by further exploration of the significance of, mechanisms involved in, and effects of increase in calcitonin during feeding in rats. 3. Identify the gastrointestinal hormone that may be responsible for increased calcitonin during feeding in rats.